1. Field of the Invention
This invention relates to a method of electroplating tubular workpieces and more specifically, an inner surface of a bent tubular workpiece, and an auxiliary anode element suitable for use in the method.
2. Description of the Prior Art
In electroplating, generally, an anode element and a workpiece to be electroplated are immersed in a plating liquid containing plating metal ions. Electric current is supplied between the anode element and the workpiece serving as a cathode element so that the workpiece is electroplated. When the workpiece is tubular, the inside of the workpiece is concealed from the anode element such that a sufficient amount of current flow for the plating is not obtained inside the tubular workpiece. Accordingly, an inner surface of the tubular workpiece has an extremely low degree of plating relative to an outer surface thereof.
To improve non-uniformity in the current flow distribution as described above, the prior art has provided use of an auxiliary anode element. The use of the auxiliary anode element is effective when the tubular workpiece is straightforward in its shape. In this case, the workpiece is placed upright in the plating liquid contained in a plating bath, and the auxiliary anode element is inserted into a hollow interior of the workpiece so as to be concentric therewith. However, the auxiliary anode element has been found ineffective for a bent tubular workpiece which is bent or curved at one or more portions in the middle thereof.
To plate the bent tubular workpiece, the prior art has provided a hot dipping in which the workpiece is immersed in a molten solder with a low melting point etc. to be plated. In this method, however, the solder is as it drops from ends of the workpiece. As a result, the hardened solder projects from the ends of the workpiece and a later mechanical finishing operation is required to remove projections of hardened solder. This complicates the plating process.